Alkyl polyalkoxy sulphates often also called alkyl polyether sulphates, (fatty) alcohol polyglycol ether sulphates or (fatty) alcohol polyether sulphates, commonly known and referenced hereunder in short as ether sulphates or alkyl ether sulphate salts, are used as surfactants or emulsifiers in numerous consumer products such as cleaning agents, shampoos and cosmetics. Structurally they have a lipophilic alkyl group and a hydrophilic area composed of the polar ether groups and the chemically bonded sulphate anion. These physical properties make these compounds surfactants and allow them to emulsify fats and oils. They are not very sensitive to hard water and are generally easily biodegradable. Fatty alcohols are understood hereunder to reference C8- to C18-branched and/or unbranched aliphatic mono-alkanols.
Alkyl ether sulphates can be produced from fatty alcohols in that fatty alcohols are initially converted with alkylene oxide, usually ethylene oxide. EO references ethylene oxide or an ethylene oxide group (—CH2CH2O—). The average number of ether groups is normally between 1 and 12. The hydroxyether is then converted to an ester with sulphur trioxide which results in a sulphuric acid monoester or a sulphuric acid semiester. This acid is unstable and is converted into a salt with the use of alkali hydroxide or ammonia. Common commercial forms in the case of sodium ether sulphates with 2 or 3 EOs are aqueous paste-like compositions with a concentration of approximately 70% by weight or aqueous liquid compositions comprising up to 28% by weight anionic active substances (in each case measured as anionic active substance in accordance with DIN ISO 2271). Concentration ranges between approximately 30% by weight and below approximately 70% by weight active content (anionic active substance) result in non-flowable and non-pumpable compositions, as liquid crystalline structures in the form of hexagonal or cubic phases with a very high viscosity are formed. These often constitute a problem when diluting 70% ether sulphate pastes, which have a lamellar liquid crystalline structure, to the desired usage concentration.
Concentrations of slightly over 70% by weight and more are also no longer flowable or pumpable as crystallisation of the ether sulphate begins, whereas concentrations of around 70% by weight are often found to be flowable and pumpable.
Several solutions to prevent very high viscosities in ether sulphates have been described in the literature, such as the use of alkyl- or alkanol-amines as neutralizing agents or addition of organic solvents like alkylene glycols or short chain alcohols or polyalkylene sulphates or nonionic surfactants such as alcohol alkoxylates as viscosity reducers. Viscosity reducers need to be present in significant amounts, meaning more than the usual residual unsulphated matter under standard sulphation conditions. This can be achieved by either intentional incomplete sulphation reaction or by adding viscosity reducers in the neutralization step.
Whereas the use of alcohol ether sulphates containing ethylene-oxy/ethylenoxide units as ether groups is well known in personal care, washing and cleaning formulations as well as in industrial applications, for example as emulsifiers for emulsion polymerisation, ether sulphates containing propylene-oxy units are less familiar on the market. To date, only up to 40% solutions of alkali fatty alcohol (poly)propoxy sulphates are available in a convenient, i.e. flowable and pumpable, viscosity range, and no supply forms which dissolve both in water and in oils are known.
For use in industrial applications such as textile and leather auxiliary agents, metal working and lubricants, oil and gas field chemicals or tertiary oil recovery, surfactants or emulsifiers are required which exhibit a high emulsifying effect for various oils with water. Products with a high active content are required in order to keep the amount used and raw material and transport costs associated therewith as low as possible. The products should also be available in the form of flowable and pumpable material which is as homogenous as possible, as this is the simplest form of transporting, storing and dispensing them for use. The products should be essentially free of organic solvents and/or other viscosity reducers, have a low salt content, mix well with water and oils and be easily dilutable to the desired usage concentration. In addition, as low a pour point as possible is desirable which allows it to be used at low temperatures.